Differential speed responsive device



May 7, 1946. H. M. McCoy 2,399,685

DIFFERENTIAL SPEED RESPONSIVE DEVICE Filed Feb. 9, 194s l'7 sheets-sheet;

. 9 499mm A f1 mmmmm May 7, 1946. H. M. McCoy 2,399,685

DIFFERENTIAL SPEED RESPONSIVE DEVICE Filed Feb. 9, 1943 7 Sheets-SheetvZ -May 7, 1946.

H. M. MccoY DIFFERENTIAL SPEED RESPONSIVE DEVICE Filed Feb. 9, 1943 7 Sheets-Sheet 3 May 7, 1946. H. M. MCCOY DIFFERENTIAL SPEED RESPONSIVE DEVICE 7 Sheets-Sheet 4 Filed Feb. 9, 1945 4 rok/ver# May 7, 1946. H. M. MccoY v2,399,685

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DIFFERENTIAL SPEED RESPONSIVE DEVICE Filed Feb. 9, 1945 7 Sheets-Sheet 6 2 PEEHTED EY CHN. /5/

Patented May 7, 1946 UNITED lsTiiTiszs PATENT OFFICE DIFFERENTIAL SPEED RESPONSIVE DEVICE Howard M. McCoy,- Faireld, Ohio Application February 9, 1943, Serial No. 475,297

16 Claims. (Cl. 264-9) (Granted under the act of March 3. 41883, as amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to improvements in difierential governors for use in the control of the speed of prime movers or as a synchronizer in maintaining a predetermined relation in the speeds of two relatively moving shafts, or plurality of prime movers.

'I'ne differential type of governor, though invented more than one hundred years ago, has never been widely used due to hunting characteristics present in the original form of the governor and' in subsequent modifications thereof of which I am aware. If we take the case of a simple differential governor, in which the differential carrier or equivalent element is either directly or indirectly employed to actuate a control element'upon displacement of the carrier in either direction from a neutral position, any departure in speed causing carrier displacement will initiate acontrol effect tending to cause the prime mover or other controlled device to return to the desired speed. The prime mover will be restored to theV equilibrium speed condition however with the control element and carrier in a position other-than the neutral position so that an over control will result which will start a continuous oscillation, the prime mover speed oscillating about the equilibrium speed value but never again attaining la constant value, and any change in load on the prime mover or other controlled device will in general make matters worse. The introduction of high viscous damping into such a control system obviously may reduce the amplitude of hunting oscillations to a negligible value but will also destroy the main advantage of the differential governors sensitivity, i. e. its ability to detect and utilize small changes in speed for initiating a control effect. ,g

I am aware that it has already been proposed in the U. S. Patent to Donald M. Berges, Serial No. 2,160,324, to employ in a propeller pitch control "mechanism a vdifferential governor to axially'shift a contact in either of two directions -to engage either of a pair of pitch changing motor controlling contacts to energize the motor, and the pitch changing motor being connected by a follow-up to shift the said pair of contacts to stop the motor upon the proper pitch correction being made. This system, however, while an improvement over prior devices, is likely to hunt, becauseV the inertia of the-pitch chansing motor will cause it to overrun the equilibrium position, which will initiate hunting.

In accordance with the present invention, a follow-up is employed which is entirely independent, so far as its rate of operation is concerned, from the movement of the controlled element. and further .the follow-up speed is adjustable to adapt the governor to any particular prime mover irrespective of its inertia characteristics. The governor in accordance with the present invention also 'differs radically from previous proposals in that the follow-up is introduced directly into the differential control unit so that the controlling element thereof is always restored to a predetermined neutral position. The governor control within a predetermined part of its control range is of the proportionalizing type, i. e. the control effect produced is-proportional to the off speed, and throughout the balance of its range the control effect may be of constant rate. Further, a governor in accordance with the invention may be constructed to include anticipating or acceleration responsive control which is very desirable for meeting certain governing requirements and by reducing time lag in the control system provides an additional antihunting feature.

The dierential governor in accordance With the invention may be used to particular advan-` tage as an engine speed control' device by controlling the propeller pitch either in single or multiengined aircraft to replace the` conventional centrifugal governor, with the advantage that in multiengined installations the need for separate engine synchronizing apparatus is eliminated, with a consequent saving of weight. Further, the governor in accordance with the invention can be adapted by regulation of its iollow-up characteristics to any prime mover control, irrespective of the characteristic time or inertia characteristics thereof.

The novel structure 'of the speed resonsive device in accordance with the present invention may also be employed as a speed indicating mechanism instead of as a governor, i. e., the mechanism is employed to position a pointer to indicate the instant speed of a rotating shaft.

It is therefore an object of the invention to provide a differential governor for controlling the speed of a prime mover in which the governor has stable governing characteristics.

It is a further object of the invention to provide a speed controlling apparatus including a differential type speed responsive means for controlling a servomotor and including restoring means operatively connected to the speed responsive means, the rate of operation of therestoring means being manually or automatically adjustable and independent of the rate of operation of said servomotor.

It is another object of the invention to provide in governing apparatus of the character described, a differential speed responsive means having a control element displaceable from a neutral position in accordance with the departure in speed of a device to be controlled from a predetermined constant speed and of follow-up means operative through the differential to restore the control element to a predetermined neutral position.

It is another object of the invention to provide speed controlling apparatus including a ating speeds of servomotor adapted to position a speed controling element, control means for the servomotor, a three-element differential having a first element driven at a constant speed, a second element driven by the device to be controlled, and a third element movable from a neutral position in response to the difference in speed between the first and second elements, operative connections between the third element and the control means of the servomotor and follow-up means operative to superimpose a correcting speed on one of said first or second elements to restore the third element to the predetermined initial position prior to or upon the prime mover's returning to the desired speed. the follow-up means being designed to prevent overrunning upon the third differential elements returning tothe neutral position.

Another object of the invention is the provision, in a dierential governor of the character described having an element shiftable from a neutral position upon a change in speed of a device such as a prime mover from a desired constant speed, of follow-up means operative to restore the said element to the neutral position prior to or at the instant when the prime mover is restored to the desired speed and in which the rate of follow-up is either constant or bears a predetermined relation to the magnitude of the speed deviation.

A further object of the invention is to provide a differential governor which incorporates means to effect an anticipatory control which is a function of the velocity or rate at which the speed of a controlled device departs from a desired speed.

Other objects-of the invention not enumerated above will become apparent by reference to the detailed description of the invention hereinafter given and to the appended drawings in which:

Fig. 1 is a schematic view, partly in section, illustrating the constructions] features of a differential speed responsive device in accordance with the invention;

Fig. 2 is a view taken on line 2-2 of Fig. 1:

Fig. 3 is an enlarged view, partly in section, illustrating details of a clutch and brake mechanism employed in conjunction with a follow-up motor of Fig. 1;

Fig. 4 is a schematic illustration of the application of the differential governor oi' Fig. 1 to the contro1 of a variable pitch propeller. and the system may readily be extended for use as a multiengine synchronizing and governing system;

Fig. 5 is a schematic view, partly in section, i1- lustrating the governor of Fig. 1 equipped with an acceleration responsive control:

Fig. 6 is a perspective view of the acceleration aacaess responsive control means of the governor of Fig. 7 is a schematic view illustrating the speed responsive mechanism of Fig. 1 employed as a speed measuring means;

Fig. 8 is a schematic view of a modification of the governor of Fig. 1 in which the speed of the servomotor and the follow-up motor is automatically varied as a function of the olf-speed condition:

Fig. 9 is a schematic view illustrating the electrical wiring of the governor of Fig. 8: and

Fig. 10 is a schematic illustrationof a further modification of the governor of Fig. 1 employing hydraulic servo and follow-up motors, the operwhich are automatically controlled in accordance with the off speed condition, this modiilcation being the hydraulic counterpart of the governor of Fig. 9.

Referring now to Fig. 1, which illustrates a differential speed responsive device or governor of general applicatie the reference character i indicates the governor generally, which includes a small constant-speed motor 2 which may be of the governor controlled type well known in the instrument art, the speed setting of the governor being adjustable by a setting knob 2a, or may be a synchronous motor supplied from a constant frequency source, the supply current frequency being adjustable to vary the motor speed, the known speed of the motor 2 being employed as a reference in the manner well known in the art. The motor 2 through a slip clutch 3 drives a shaft 4 which is suitably rotatably mounted for rotation in bearings carried by supports l which form a part of a casing structure (not shown) which encloses the governor mechanism. The shaft l has an elongated gear S pressed thereon and rotatable with the shaft, the gear t meshing with a pinion gear 1 which is internally threaded. to

form a nut which is mounted on the threads t of a shaft I which is parallel with the axis of shaft 4 and gear I, and also rotatably supported by the casing structure l, the pinion nut 'i being slidable along the teeth of gear 8. The shaft l adjacent the ends of the threaded portion is made the same diameter as the root diameter of thc threads so that the pinion nut 'I may rotate freely thereon after running oi! the threads l. Small compression springs 9a and 9b secured to the shaft l insure that the pinion nut 1 will ratchet in contact on the ends of thread 8 if it runs off at either end thereof.

'I'he threaded shaft 9 has an extension shaft I0 formed integral therewith, on the outer end of which a bevel gear I I is secured, the gear II forming one of the side gears of a differential, generally indicated by the reference numeral I5. 'I'he side gear I l meshes with a pair of bevel planet pinions I2 whichare rotatably mounted on studs Il fixed to a housing or carrier Il. The carrier I4 is provided with a suitable central bearing hub which provides for free rotation of the carrier about the axis of shaft I0. The carrier or housing Il is closed at its outer end by a gear Il having a central bearing hub and having its toothed periphery projecting beyond the housing Il, the gear teeth serving as a means to rotate the carrier Il. The differential unit I5 is completed by a second bevel side gear I1 which meshes with the Planet pinions I2 and is secured on the inner end of a shaft I8 which is rotatably journalled in the bearing hub of the gear It. Shaft Il is suitably rotatably journalled in a bearing supported by the casing structure l and has a driven clutch disc I3 secured to its outer end. The disc Il is engaged by a friction disc 23 made of any suitable material giving the proper coefficienty of friction. this disc being secured to a driving disc 2i which has a hub 22 slidably keyed to a sleeve 33. An annular compression spring 34 which surrounds the hub 22 applies an axial force to the plate 2| and friction facing 23 suilicient to transmit drive from the sleeve 23l to the shaft i3, but under abnormal torques permits slipping. The spring 24 at its outer end engages an abutment 23 formed integrally with the driving sleeve 23, the latter beingpinned to a driving shaft 23 which may be drivingly connected to the device such as a prime mover, electric motor, or the like, which is to be controlled.

If we assume that gear I3 and carrier I4 of the differential I3 are to be held stationary, rotation of shaft 23 in the direction indicated by the arrow will through clutch elements I9-20-2I drive shaft i3 in a corresponding or clockwise direction, which in turn will cause rotation of side gear I1, winch through planet pinions I2 will rotate the side gear il and shaft I in an opposite or counterclockwise direction. Counterclockwise rotation of shaft I Il will correspondingly rotate threaded shaft 9 and cause an axial feeding movement of pinion nut 1 to theright as seen in Fig. l. .If the pinion nut 1 is rotated in a counterclockwise sense by a clockwise rotation of the elongated gear 3, which rotation is imparted from shaft 4 when driven by motor 2, no feeding movement of the pinion nut 1 along the threads 8 of shaft -9 will result provided pinion nut 1 is rotatedl at the same speed as threaded shaft 9.

If the pinion nut 1 is initially in the middle of the threaded portion 3 of shaft 9, and shaft 26 should increase in speed from a speed equal to, or in a predetermined ratio to, the speed of constant-speed motor 2 as determined by the ratio of gearing between gear 6 and pinion nut 1, the pinion nut 1 will move axially Ito the right with a velocity dependent upon the number of threads per inch of threaded shaft 9 and also on the magnitude of the speed variation or ofi'speed of shaft 23 from the desired constant speed. Similarly, a reduction in speed of shaft 26 from the desired value will cause an axial feeding of pinion nut 1 to the left from the neutral position as seen in Fig. 1.

If the gear I 1 of the differential I5 is assumed to be stationary and carrier I4 rotated by gear I3 in a, clockwise sense, planet pinions I2 will rotate in a clockwise sense looking from above and will cause a clockwise rotation of side gear Il with a velocity equal to twice the speed of the carrier I4. Rotation of the carrier i4 in the counterclockwise sense will produce rotation of side gear Il in a corresponding direction. If now shaft 26 be considered as rotating in the direction of the arrow (Fig. 1), and differential carrier i 4 is rotated in a clockwise sense, the speed of shaft l0 will be decreased from the speed it would otherwise have with the differential carrier locked, and similarly the speed of shaft l0 will be increased by counterclockwise rotation of carrier I4 above the speed it would have as imparted through the differential i5 from shaft 23.

It should be noted at this point, however, that the proper action of the follow-up drive can only be obtained by proper design of the clutch elements |9-25, i. e. the minimum torque which must be developed by the follow-up motor 33 must be slightly greater than the torque required Further movement of the shifting co1lar-29 willV j engage the clutch teeth 43 and 4I and drivingly screw-shaft 3, pinion nut 1 as it slides to and fro in its operating cycles. The clutch must not slip when the follow-up motor applies its maximum torque, yet the clutch must be able to slip in the event of a jam in the governor mechanism. In the event that the clutch should slip during operation of the follow-up motor, a hunting condition may result and experiment has shown that if the clutch can transmit a torque approximately twice the friction torque of the driven elements without slipping. satisfactory operation will be obtained. In thev event that the speed of the device to be controlled is imparted to the governor through the medium of an electrical motion transmitting means of any of the types well known in the art, the slip characteristics must be the equivaient of the clutch as above noted and in this case the clutch would be eliminated.

It is thus seen that the speed of the output shaft I3 of the differential I3 will be in accordance with the algebraic sum of the separate speeds imparted thereto due to rotation of the differential carrier I4 and from shaft 23. This function of changing the speed of the output shaft I0 through rotation of the carrier I4 of the differential is employed in a novel manner to create a follow-up action tending to always restore pinion nut 1 to its predetermined neutral position after a displacement thereof, which will be hereinafter more fully explained.

In order to cause rotation of the carrier i4 of differential i3 to cause the above-noted followup action. the gear I3 meshes with a. small pinion gear 21 mounted on a shaft 23 which forms the output member of a clutch mechanism generally indicated by the reference numeral 30. The input drive to clutch 33 is derived from a small electric motor 30 hereinafter termed the follow-up motor.

Referring to Fig. 3 the clutch mechanism 33 is seen to include a. clutch shifting collar 29 which is slidably keyed to the output shaft 28 and has an annular groove 3l into which shifting pins 32 are adapted to project. The-pins 32 are carried by a shifting yoke 33 pivotally supported as at 34 and having its lower end pivotally connected to the plunger of a solenoid 33 which includes a loading spring 38. The shifting collar 29 has integrally formed therewith at its outer end a disc 31 which on its inner face is adapted to normally engage an annular brake disc 33 which is secured to a stationary annular backing plate 39 which is further supported by the clutch housing. The front face of the disc 31 is provided with projecting clutch teeth 40 which are adapted to be engaged with corresponding teeth 4| formed on a driving clutch disc 42, the latter being secured on the inner end of a shaft 43 which is rotatably journalled in a suitable bearing supported by the clutch housing. A large gear. 44 is mounted on the outer end of the shaft 43 tovdrive the same. A small gear 45 mounted on the armature shaft of the reversible electric follow-up motor 33 drives the gear 43.

The follow-up motor 33, which may be of the vsplit field reversible type, has the solenoid 35 connected in series with the armature lead thereof so that whenever the motor 33 is energized the solenoid 33. is also energized so that the solenoid plunger will pull on the shifting yoke 33 against the resistance of spring 33 and release the clutch disc 31 from engagement with the brake disc 33.

connect the output shaft 23 to the motor-driven to overcome the friction of the differential drive shaft 43 and in a. direction opposite the direction of rotation of motor 60. When motor-Il. and solenoid LIS .are de-energized. the force exerted by spring 38 on the shifting yoke 8l will cause the clutch disc I1 to move to the disengaged position, where it contacts brake 38 and prevents further rotation of shaft 22, and the gear 21 then serves to lock the differential carrier il against rotation. The pressure exerted by spring J8 and the brake disc I8 is so chosen that torques applied to the diiferential I5 by shaft Il will not cause slippage.

It has been described above how differences in speed of rotation between shaft 2B, driven by the device to be controlled, and shaft l, driven by constant-speed motor 2, will cause shifting of the pinion nut 1 in either direction from its neutral position and the means for utilizing the movement of the pinion nut as seen in Figs. 1 and 2 will now be described. A small carriage 52 is slidably mounted on parallel guides Il so as to move parallel with the axis of the threaded shaft or screw 8, and the carriage is provided with downwardly depending projections I4 which are provided on their lower ends with rollers 55 which respectively engage the pinion nut 1 on its opposite end faces and transmit movement of the pinion nut 1 into a corresponding translatory movement of the carriage B2. A pair of snap-action switches 58 and 51 are mounted on the upper side of the carriage 52 and are movable therewith. The switches 56 and 51 are provided with longitudinally extending, pivotally mounted operating levers 58 and 5l respectively, the levers being provided at their outer ends with rollers B and il respectively. The levers 58 and I9 are adapted to engage respective switch-operating plungers B2 and 6l (see Fig. 1). The switches Il and 51 are of a we1l known snap-action type such that a deflection of the operating plungers of only a few thousandths of an inch will actuate the switch mechanism and allow a limited further movement of the plungers, or overtravel. The rollers B and Si respectively engage cam plates 84 and 6l which are mounted in a parallel spaced relation and which have respectively lower dwell portions 64a and 65a, rise portions 64b and "b and upper dwell portions 64e and 65e. The above-noted cam portions are respectively disposed on opposite sides of the vertical centerline representing the neutral or mid position of the pinion nut 1. Movement of the carriage 52 to the right (Fig. 1) will cause roller 60 to engage the cam rise Mb to depress the switch lever 6l which will actuate the plunger 62 to thereby actuate the snap-action contact mechanism of switch 58. The downward movement of plunger B2 will continue until the dwell portion Mc of cam 8l is reached, and thereafter further movement ofthe carriage 52 to the right will produce no further eii'ect on the switch. While carriage 52 is moving to the right from the neutral position, the roller Il engages the lower dwell portion a of cam l so that switch 51 is not operated. In a similar manner movement of carriage 52 to the left (Fig. l) from the neutral position causes operation of switch lever 59 to operate switch l1 but allows roller 60 to ride on the lower dwell portion a of cam 64, leaving switch 56 inoperative.

Referring to Fig. l, electrical connections are made to the switches il and 51 through flexible pig-tail leads, not shown, and one pair of respective switch terminals are connected in parallel to ground by means of a conductor 1I, and the remaining pair of switch terminals are re spectively connected by means of conductors 'I2 and 1I to respective conductors 1I and 1l. The conductors I4 and 1I are connected at one end to the respective field terminals of the follow up motor l0. The amature conductor 'It of the follow-up motor III is connected in series with an adjustable rheostat 11 to the positive terminal of a battery or other current source 1l, the negative terminal of which is grounded. A conductor 1l, also connected to the positive terminal of battery 1l, is connected to the armature lead of a split field or other type reversible electric servomotor l0, which has its field or other reversing terminals respectively connected to the remaining ends of conductors 14 and 1I. It is thus seen that the reversible follow-up motor ll and the reversible servomotor Il are connected in parallel and controlled as to direction o! rotation by switches ll and l1, the speed of rotation of the follow-up motor Il being determined however, by the setting of the adjustable rheostat 11. The speed of the follow-up motor is usually limited so that the follow-up rate remains less than either the master motor 2 or the shaft 2B. The follow-up rate in extreme cases, involving large moments of inertia of the prime mover and hence large time lags may be greater than that of the master motor 2. In any case it is adjustable by means oi.' variable resistance 11 to any desired or necessary follow-up rate to secure proper governing operation. It is also to be understood that in place of the single variable resistance 11 separate adjustable resistances may be placed in series with each neld coil of the follow-up motor to obtain a different followup rate in one sense of governing control than in the other to take care of those cases where the response rate of the device being controlled is different in one direction than the other. One example being in control oi' engine speed through a variable pitch propeller in which the centrifugal torque on the blades assist in changing pitch in one direction and oppose a pitch change in the opposite direction.

The servomotor l0 has its armature shaft Il provided with a worm l2 which meshes with the teeth of a gear sector 8l rotatably mounted as at 84 and provided with an actuating lever Il which may be connected in any suitable manner to the speed-controlling means of the prime motor or other device to be controlled in a manner well known in the art.

Ormui'non The operation of the differential speed responsive device of Fig. 1 when employed to control the speed of rotation of a prime mover or other mechanism such as an electric motor, hydraulic power transmission, or the like is as follows:

The shaft 28 is directly or otherwise connected to the device to be controlled so that the shaft 2l will rotate at a speed equal or proportional to the rotational speed of the controlled device. The lever .I is suitably connected to the speed control element such as an engine throttle valve, electric motor controlling rheostatl hydraulic control valve, or the like, such that movement of the control lever 8i in opposite directions from a neutral position will cause an increase and decrease respectively in the speed of the controlled device.

The speed of motor 2 is then adjusted to a value such that shaft l drives pinion nut 1, through gear i, at the desired rotational speed of the device to be controlled, and assumed to be in the direction of the arrow in Fig. 1, and if the screw shaft i is beins rotated in the direction of the a,soa,oss

'I from the neutral position as previously exf plained and servomotor l and follow-up motor l0 will be de-energized. If shaft 28 should lncrease in speed from the desired constant speed,

pinion nut 1 will rotate relative to the threaded shaft l and will move along the threads l axially towards the right, causing switch I6 to be actuated in the manner previously explained. The switch 56,-upon closure of the contacts thereof, will, through conductors 13 and 1I, immediately energize the servomotor l0 to run in a direction such that control lever II will move the control element of the controlled device in a direction to reduce the speed of the said device and cause a corresponding decrease in the speed of shaft 26.

Simultaneous with the energizing of servomotor l0 the follow-up motor 50 is also energized and lthrough the clutch mechanism 30, previously described with reference to Fig. 3, will cause rotation of the output shafts 2l and gear 21 in such a direction that gear l 6 and differential carrier I4 will be rotated in a clockwise sense as viewed from shaft 28 looking to the left. 'I'his rotation of the diiferential carrier I4 will cause a reduction in the speed of rotation oi.' shaft I0 of a constant amount depending on the speedof follow-up motor 50 as determined by the setting of the speed-control rheostat 11 thereof. If the departure of the rotational speed of shaft 26 from the desired speed, known as the olf-speed, is of small magnitude, the decrease in speed of shaft III due to the follow-up drive will exceed the amount of increase in speed thereof transmitted from shaft 26, and accordingly the screw shaft 9- will lag behind the pinion nut 1 and the motion of the latter will be reversed returning the same axially toward the left until it is again in the neutral position allowing switch 56 to return to its initial open position de-energizlng servomotor Ill and follow-up motor l and through clutch mechanism 30 locking the carrier Il of differential I5 and allowing the shaft Ill to return to the same speed of rotation as shaft 26.

as to cause clockwise rotation of the diiferentiai carrier Il, causing the speed of shaft Ill to be increased to restore the pinion nut 1 to its initial neutral position.- 'I'he repetition of control cycles will be the same in character, depending on the value of the off speedl as for the overspeed condition.

It will be noted that after the value of the oil' speed exceeds a predetermined follow-up speed, the follow-up is not capable of introducing a suillcient increase or decrease in the speed of shaft I0 and screw shaft 9 to offset the effect of the off speed so that the pinion nut will thereafter continue its movement to the right or left of the neutral position, depending on whether the oil speed is an overspeed or underspeed condition. Under such circumstances the switch 56 or 51 will remain closed so that servomotor 80 will operate continuously until the eifect on the controlled device becomes effective yto change the speed of shaft 28 sufficient to allow the follow-up drive to restore the pinion nut to the neutral position. In the event that the pinion nut runs on the threads l, it will continue to rotate on one of the thread root diameter portions of shaft 0 ratcheting against the ends of the thread due to the action oi' either of the buffer springs 9a or Sb.- As soon as the servomotor 80, then operating atits maximum rate, reduces or increases the speed of shaft 28, as the case might be, to a point f where the follow-up speed becomes dominant, the

After completion of the above cycle, servo- I ,motor 8l will have made an adjustment on the speed control of the device being controlled, tending to diminish its speed of rotation, but if the control eifect was insuiiicient, the remaining oil speed will cause the above cycle to be repeated a number of times until the device to be controlled is restored to the desired constant speed. It will be noted that since the follow-up speed is substantially constant, the time duration of each-- control cycle will decrease in proportion to the off-speed, as the 'off-speed decreases, so that servomotor Bil applies a decreasing control movement until the final position is reached, where the speed of the control device is exactly the desired value.

When the speed of shaft 26 falls below the predetermined constant speedthe operation of the device is exactly the reverse of that described above. i. e., such a condition will cause a decrease in the speed of screw shaft l relative to pinion nut 1 so that the same will be moved to the left from its neutral position, thereby actuating switch 51 to complete a circuit through conductors 12 and 14, causing servomotor Il to be enersized to rotate in a reverse sense from that as above described, to thereby cause the controlled device to increase its speed. The follow-up motor II will'also operate in the opposite direction so pinion :nut 1 will be returned to its neutral position and the final speedcorrection will proceed in cycles as above described. The follow-up rate may be adjusted so that it is possible that servomotor will, during the maximum displacement of the pinion nut 1, have produced an overcontrol effect so that the pinion nut 1 will move, due to follow-up action, past the neutral position in the opposite sense, causing the character of the control to be reversed to cancel the overcontrol. 'I'his action will cause several oscillations in the speed of the controlled device about the equilibrium position; but the amplitude of such oscillations will be continually reduced, since the follow-up action will produce an effect similar to damping. For many types of governing installations this character of control is preferable, since the time required to reach equilibrium speed is a minimum.

It will be evident from the above description of the governor of Fig. 1 that the` same operates on the proportionalizing principle, i. e., that the control en'ect produced is proportional to the required control, i. e., to the existing olf-speed condition, but the proportionalizing is with respect to time, since the time duration of each control cycle within the normal governing range is proportional to the value of the off-speed at the beginning of the cycle.

In control installations where oscillations about the equilibrium speed are undesirable, the follow-up speed of motor 50 may be made sumciently high that the pinion nut 1 may always be returned to the neutral position irrespective of the value of the oif speed, so that the governing action will be` aperiodic or dead beat, i, e., upon any departure in speed of the controlled device from the desired speed the governor will cause -a progressive speed correction to be made which will, if plotted as a curve against time, terminate at the equilibrium speed value. Such operation will necessarily involve approaching the equilibrium speed in steps of decreasing magnitude, which will accordingly increase the total time required to restore the controlled device to equilibrium speed.

It is thus seen that by adjusting the speed of operation of the follow-up motor 50 through rheostat 11, it is possible to obtain Widely varying governing characteristics so that the same Sovernor without change may be applied to the control of a large number of devices, each having a different governing requirement, this feature being of particular value in the control of variable pitch propellers for aircraft, since one type governor can be employed regardless of the inertia characteristics of the particular engine-propeller combination.

In order to illustrate the application of a governor of the type illustrated in Fig. 1 to the con- I trol of the speed of a prime mover such as an aircraft engine by controlling the pitch of the propeller blades, reference is made to Fig. 4 in which the controllable pitch propeller is generally indicated by the reference numeral 90 and having the adjustable pitch blades 9| adapted to be ad justed by a reversible electric motor I2 in a manner well known in the art. The propeller ll is driven by the crankshaft 93 of a conventional aircraft engine 95. An altemating-current generator 98, driven by the engine, delivers current by means of conductors 91 to synchronous electric motor 98 which thus runs at a speed equal or proportional to the rotational speed of engine 8l. This particular means for transmitting engine speed to the governor may be replaced by any other suitable type motion-transmitting means, such as a flexible shaft drive, a Selsyn transmitter and receiver, or a contact interruptor device driven by the engine and adapted to control an impulse motor or the like. The synchronous motor 98 is directly connected to the shaft i8 of a governor i of a character identical with the governor of Fig. l, the electrical transmission permitting slip and thus eliminating the necessity for shaft 28 and clutch i92i. The conductors 1l, and 19 are connected through the usual brushes and slip rings to the reversible pitchchanging motor 92 which then serves as the equivaient of the servomotor 80 of Fig. l.

The speed setting of constant-speed motor 2 is adjusted by actuation of the speed-setting control knob 2a so that it corresponds with the desired engine speed, and if the engine departs from this speed, governor i will energize the pitchchanging motor 92 to effect a change in the pitch of the propeller to restore the engine to the desired speed. The regulating characteristics of the governor i are adjusted to suit the particular engine-propeller characteristics by means of the rheostat 19 which controls the speed of the follow-up motor as previously described with reference to the device in Fig, 1. The operation of the governor in Fig. 4 in no way differs from that as previously described.

The arrangement of Fig. 4 may be extended to use as a combined governing and synchronizing system for a plurality of engines by simply providing a separate governor unit of the character described for each engine and driving the constant-speed side (shaft l Fig. l) of each governor from a common constant reference speed motor. In this arrangement all the governor units would be mounted in a single casing, and all of the constant speed driving shafts would be connected by bevel gears or the like to a single shaft driven by a constant-speed motor such as motor 2, Figs. 1 and 4. If then any motor departed in speed from the desired speed, its sepasoaess arate governor unit would react to adjust the pitch of the propeller associated with the said engine to cause the engine speed to be restored to equilibrium with the selected reference speed. Since all of the governors would employ a common reference speed, all of the engines will be maintained in synchronism so far as speed of rotation is concerned. As an alternative, one engine may be employed as a reference speed source to drive the reference speed sides of the governors for the remaining engines so that the controlled engines will follow the speed changes of the master engine, the latter being controlled by a separate governor which may differ from the type herein disclosed.

As an alternative arrangement, a separate governor may be mounted on each engine to be directly driven thereby and the constant speed sides of the governors being driven from a single ad- Justable constant speed source by remote drives.

It should also be understood that where the governor of Fig. l is applied to control an electric servomotor on which the load is heavy, such as the electric propeller pitch changing motor of Fig. 4, the governor controlled switches may be employed to close relays which in turn are operative to control the energizing of the servomotor, thus avoiding transmitting heavy eurrents through the governor controlled contacts or switches. Since the above modes of synchronizing engines are readily apparent, no illustration thereof is believed necessary in the,draw

ings. l

The governor of Fig. l,A as previously explained, operates in a series of cycles when the off-speed is below a predetermined value, and

. this is true even though the rate of change of speed of the controlled device is large so as to cause a sumcient accumulation of off-speed revolutions to eventually cause the servomotor to operate continuously at its maximum rate. It is well known in the art of governing the minimizing of time lag in the governing system is essential but that this cannot usually be accomplished without affecting the stability of the governor. However, if a separate means is employed, responsive to the rate of change of speed of the device to be controlled which is effective to impart an immediate control upon the rate of change of speed exceeding a predetermined value, the time lag can be reduced to a minimum without adversely affecting the stability of the governor. Such combined governors in the prior art have usually consisted of centrifugal weights which are so arranged as to also respond to accelerations, as well as the change in speed, of a flywheel or the like to which the governor is attached, or comprised a combined gyroscopic and centrifugal governor.

So far as I am aware, however, it has never been proposed to employ an acceleration-responsive or anticipatory control means in combination with a differential type of governor, for the reason that the oscillatory nature of the control of such a governor would render the accelerationresponsive means ineffective and the latter would make the oscillation problem worse. The combination of a differential governor, however, of the character of the present invention which, due to the provision of the novel follow-up, is inherently stable, with an acceleration-responsive control means, gives a combination which overcomes the lack of rapid response above noted when the rate of change of speed of the controlled device is large, but also greatly reduces the total time required to attain equilibrium speed oon'- ditions and. in fact. adds to the anti-hunting v characteristics oi' the governor.

'Ihe provision of the anticipatory control means toa governor o! the character oi' Fia. l is illustrated in Fig. 5, in which parts common to Fig. l are indicated by the same reference numerals. v'I'he anticipating control means. as seen in Figs. 5 and 6. comprises a small flywheel or inertia element Ill, freely rotatably mounted by means of a ball bearing IUI on the shaft I8, the flywheel IUI being provided with a pin |I2, which projects through an arcuate aperture |03 in a disc |84 of insulating material, having a hub Ill secured to shaft |l to rotate therewith. The pin |02 is yieldingly connected `by means of adjustable tension springs I to the disc |04 so that the flywheel is caused to rotate with the disc. but any acceleration or deceleration of shaft II will cause flywheel to rotate relative to disc |04 and shaft i8.

As seen in Fig. 6, the flywheel |00 is also provided with a second pin Ill projecting through a second arcuate aperture Il! in the driving disc |04. and this pin carries a double electrical contact lll, which is adapted to engage either of a pair of adjustable contacts |I| and ||2 respectively disposed on opposite sides thereof. The contacts Ilil, t||| and H2 are respectively electrically connected by flexible leads to slip rings H3, I|4 and |15, which in turn are engaged by -brushes Ill, ||1 and il. respectively. Brush IIB is connected to ground and yhence serves as a connection to the grounded terminal of the battery 18. Brush II'I is connected to conductor 15 beyond the connection of conductor 1I thereto,sothat contacts lil and Iii serveasaswitch means connected in parallel with switch I6 and operative to energize the servomotor Il, irrespective of whether switch 5l is open or closed. Similarly, brush Ill is connected to conductor 14 beyond the connection of conductor 12 thereto. so that contact means H0 and ||2 serve as a switch connected in parallel with switch l1 and operative to energize servomotor Il independent oi' whether switch Il is open or closed.

Operation of anticipatory control The tension of springs |06 is initially adjusted so that predetermined vahies of acceleration or deceleration of shaft Il will not cause the inertia element to rotate relative to shaft Il and disc |04 an amount sufficient to cause .engagement of contact Il! with either of contacts and ||2. The governor in this range will then operate exactly as described with reference to Fig. 1.

If the shafts and IB, however, are accelerated beyond the predetermined value, inertia element III will lag behind shaft Il and disc |l4 and will tension one of the springs I sufilcient to cause contacts |||i and to engage, which will energize servomotor I0 to rotate in the same sense as when energized by switch IB but to operate at its maximum rate to apply a correction tending to reduce the speed of the device being controlled. 'I'he remaining portions of the governor I will operate in the previously described manner, but the actuation of switch il will not affect the operation of motor Il as long as the acceleration or rate of change of speed exceeds vthe predetermined value. When the servomotor Il -has operated for a sufllcient length of time to reduce the acceleration of shafts 2l and Il below the predetermined value. the tension of the active spring I" will overcome the inertia lag of the element |04 and will cause disengagement of contacts llt and Iii. thereby restoring the control function to the governor structure of Fig. 1. which will then function in the manner above described, i. e.. if the accumulated value of the olf-speed revolutions is sumcient to cause continuous movement of the pinion nut l to the 'right from the neutral position or to have actually run oi! the thread on shaft 9, servomotor I0 will continue to operate at its maximum rate. If the oil-speed revolutions accumulated during operation of the accelerationresponsive means do not exceed a predetermined value, the control will be of the interrupted character as previously described. until the equilibrium speed is reached.

If the 4device .being controlled should cause a deceleration of the shafts 2C and i8 beyond the predetermined value, the inertia element |00 will tend to continue rotation at the equilibrium speed and will tension the other oi' the pair of springs |08 suillcient to allow contact |||l to engage contact ||2 to cause servomotor 80 to be actuated in the reverse sense from that as above described, causing the servomotor to adjust the speed-control means of th'e controlled device to increase the speed thereof. 'I'he contacts IIC and ||2 will be disengaged when the deceleration is reduced to the predetermined minimum value, and the governor will thereafter be elective through switch 51 to dually restore the controlled device to the desired equilibrium speed.

It *will be noted that the particular value of equilibrium speed selected has no effect on the anticipatory control, since the inertia relement |00 respondsy only to accelerations or decelerations, i. e., to rate of change of speed, and by this token is also independent of the magnitude of the oK-speed. The acceleration-responsive device, being rate-responsive, is able to anticipate large speed departures and initiate a corresponding corrective influence before the governor proprer can respond and thus reduces the time lag in the control system to a minimum. thereby bringing the governor-control response more closely in phase with the speed changes and materially reducing any tendency to hunt.

It is to be understood that a differential governor provided with anticipatory control can be applied to control variable pitch propellers or for any other purpose to which the governor of Fig. 1 is applicable.

Fig. 7 illustrates the adaptation of the speedresponsive device of Fig. l to use as a speed-measuring means, and in this ligure all parte common to that of Fig. 1 are indicated by the same reference numerals as in Fig. l.

Referring to-Flg. 7, the shaft 4 and gear I are driven by an electrical self-synchronous receiver |20 such as a Selsyn. the rotor of which in turn is driven in synchronism with' the rotor of a. corresponding remote self-synchronous transmitter |2| electrically connected to the receiver. The rotor of the transmitter |2| is driven by gear |22 and idler gears |23 from a ring gear |24 mounted on the shaft |28 which may, for example, be the propeller shaft of a ship. In the event that shaft |25 is reversible as to rotation, an automatic driven at a speed proportional to the speed of shaft |28.

The shaft 28 of the speed-responsive mechanism I, instead of being driven by a controlled prime mover, is driven by a small, variable-speed, electric motor |28, whose speed is automatically adjusted, so that, so long as shaft |38 'rotates at a constant speed, motor |28 will be driven at a speed proportional thereto, and is effective to drive screw shaft 8 through the medium of shafts 28 and I8, differential |8,.and shaft I8, so that pinion nut 1 does not move axially on threads l. The motor |28 is controlled as to speed of rotation by a variable resistance unit |21, having a resistance winding |28, one end of which is grounded and the winding is engaged by a wiper arm |28 which also wipingly engages a circular contact strip |38 connected by conductor |3| to one lead of motor |28, the other lead of which is conm nected to the positive side of battery 18. The wiper arm |28 is fixed to a rotatable shaft |33 which has a gear |33 fixed to one end and driven by a worm 82, in turn driven by servomotor 88 as in the device of Fig. 1. The outer end of shaft |33 has a pointer |38 affixed thereto which is adapted to cooperate with a dial |38, having suitable speed indicia thereon. The device of Fig. '1, except as above noted, is identical with that of the governor of Fig. 1 employing the same form of control of the servomotor 88 and follow-up motor 88.

Operation of the device of Fig. 7

The rotation of shaft |28 is electrically transmitted to the gear 8 as above described, which rotates pinion nut 1 on the threads 8 of shaft 8, and if shaft 8 is rotated in the proper direction and at the proper speed, the axial feeding movement of pinion nut 1, due to rotation thereof by gear 8, will be offset by the contrary feeding effect of the rotation of shaft 8 by shaft |8, through differential I8, from input shaft 28, the latter being driven by motor |28. For the particular equilibrium of speeds between motor |28 and shaft |28 there will be a corresponding dennite position of the rheostat wiper contact arm |28 and shaft |33, so that pointer |38 will indicate the existing speed of shaft |28.

If, for example, the speed of shaft vI 28 increases, pinion nut 1 will move axially toward the left from its neutral position and close the contacts of switch 58, which will energize servomotor 88 to run in a direction to drive shaft |33 in a clockwise direction, cutting out resistance in series with motor |28 so that the latter increases its speed. The follow-up motor 58 will be energized to restore the pinion nut 1 to its neutral position upon energizing of motor 88, in exactly the same manner as described with reefrence to Fig. 1, so that the speed of motor |28 will be increased in a. series of steps until it is in equal, or proportional, equilibrium with the existing speed of shaft |28, and pinion nut 1 will then remain in th'e neutral position with servomotor 88 de energized. The pointer |38 will have moved to a new position corresponding to the new speed value of shaft |28.

If the speed of shaft |28 decreases, the operation of the speed-responsive mechanism will be reversed from that as above described and servomotor 88 will be operated in a series of steps to cause the resistance contact arm |28 to rotate in a counterclockwise sense until sufficient resistance has been inserted in the circuit of motor |28 to reduce the speed of the same to correspond to the reduced speed of shaft |28, and accordingly. pointer |38 will indicate, relative to dial |33.

the new speed of shaft |28.

It is thus seen that the speed of motor |23 is always so controlled by the speed-responsive 'device I, that it is proportional to the existing speed of shaft |28 and the setting of the speed-control rheostat |21 can be interpreted in terms of a speed indication. The speeds to be indicated may range from a predetermined low-speed value to the maximum likely to be encountered, and the motor |28 and its associated speed control is selected for the particular speed range for which the device will be employed.

In the speed indicating device illustrated in Fig. '1 the dial |38 would be calibrated for some particular temperature condition and if the ambient temperature varies considerably from the calibration temperature, it is evident that the change in resistance of the windings of the motor |28 and change in the resistance of the speed control means |28 will cause some error in the indicated speed. Where variations in the ambient temperature are such that temperature error compensation is necessary, the error in indication can be substantially corrected by arranging the pointer |38 for free rotation on the end of shaft |33 and coupling the pointer to the shaft by a coiled bimetallic strip which can shift the pointer relative to the shaft |33 an amount to compensate for the error of speed indication due to change in the ambient temperature. This means of securing temperature compensation is well known in the instrument art, being widely employed on altimeters and the like and' forms no Dart of the present invention.

` Fig. 8 illustrates a modified form of the governor of Fig. 1, in which the rotational speed of the servomotor and the follow-up motor are respectively controlled in proportion to the existing olf-speed so as to further increase the stability of the novel differential governor in accordance with the invention. In this modification, parts common to the device of Fig. 1 are indicated by the same reference numerals as in the latter figure. The modified form of governor of Fig. 8 employs the same type of follow-up as employed in the device of Fig. 1, but employs a conventional differential as the speed difference measuring means and employs speed-control means for both the follow-up motor and servomotor.

Referring to Fig. 8, the constant-speed motor 2 drives the shaft 3 through a slip clutch 3', and shaft I8 is driven through differential I8, shaft I8, slip clutch 28, and shaft 28 in the same manner as in the device of Fig. 1, follow-up motor 88 being adapted to drive through diiferential I8 in the same manner as in previously described embodiments. 'I'he shafts 3 and I8 are respectively connected to bevel side gears |3| and |32 of a conventional differential, generally indicated by the reference numeral |38, the side gears meshing with bevel pinion gears |33 mounted on a rotatable carrier |33, which has formed thereon a helical toothed gear |38 which meshes with a corresponding gear |38. As long as shafts 3 and I8 rotate in opposite directions at equal speeds, carrier |33 will remain stationary, but upon any dii'ference in speed of the said shafts, the carrier will begin to rotate at a speed equal to one-half the difference in speed of the differential side gears and in the direction of the gear having the greater velocity. causing gear |33 to rotate about its axis. The differential |38 is the equivalent of the gears 3 and 1 and screw shaft 8 of Fig. 1, the angular displacement of gear |33 by the rotation Y or Fig. 1.

Gear |46 is adapted to drive a shaft |41 which, through anbre sleeve |40 forming a slipdrive, drives a hubv|46 which has two cams |50 and |5| rigidly mounted thereon. The cam |50 has a portion a-b of constant radius and has iianks of increasing radius from points a and b to a stop portion |52. Cam |60 engages a pair of contactengaging plungers |51 and |61, symmetrically disposed on opposite sides or the vertical centerline of the cam and adapted to be alternately depressed upon counterclockwise and'clockwlse rotation, respectively, of the cam |50, as seen in Fig. 8. The plungers |51 and |61 are depressed an amount proportional to the rotation of cam |50 from the neutral position, which in turn dedifferential |40, in accordance with 'the existing speed difierence or oil-speed.

Thek plungers |151 and |61 are adapted to respectively actuate resistance cut-out contacts in units indicated by the reference numerals |56 and |66 respectively and are respectively electrically connected to resistance umts |53 and |63, the control contact and resistance unit assemblies being generally indicated by the reference numerals |55 and |65, since such assemblies form a weiltrically connected to control the energizing of the servomotor 00, which is adapted to' control a prime mover or the likeas described with reference to the embodiment of Figs. 1 and 4. The speed-control unit |15 is adapted to control the speed of the follow-up motor 50, so that the follow-up speed is proportional to the existing value of the oil-speed, so that the control of the servomotor is substantially in a. series of cycles throughout the normal range of speed control.

The electrical circuits of the device of Fig. 8 are illustrated schematically in Fig. 9, and as seen in this gure, the motor-speed-control unit |55 has a resistance unit |53 consisting of a serially connected group of resistances which are connected to a series of exible contact arms |56, each of whichis provided with a. contact |56 on its lower end; the contacts being adapted tov be successively engaged 4upon depression by the contact plunger |51. 'I'he first contact arm of the series is connected directly to the field coil lead 14 of the servomotor 00, so that engagement of the first contact |50 with .the second contact, serves to connect the field of motor through the entire' resistance unit to ground, whereby a return circuit is completed to the grounded terminal of battery 16. The plunger |51, as it is deflected, causes engagement of additional contacts |56, which causes resistance units to rbe successively shorted out, thus reducing the total resistance in the servomotor circuit. causing a corresponding increase in speed for a given direction of rotation of the motor.

The first pair of contact arms |56 carry additional contacts |60 and |6| respectively, which when closed connect one follow-up motor 50 field coil terminal lead |54 directly to ground, thus connecting the same to the grounded terminal of battery 10, so that motors 50 and `80 will start substantially simultaneously each in one direction of rotation. I

The speed-control unit |65 is identical in construction with unit |55, and includes serially connected resistances |63 connected to the iiexible contact arms |66, thelatter carrying contacts 66, all except the first pair,being adapted when successively closed of shorting out successive resistpends on the angular rotation of gear |46 by,`v

, shown) to decrease its. speed, and simultaneous lileldl terminal of servoxnotor through lead 15 to ground to complete the circuit to the grounded terminal of battery 10. The first pair of contacts |66 is operative as a switch to connect the entire series of resistance units |63 in series with the tleld terminal lead 15 of motor 80. The plunger |61, upon deflection thereof by cam |50, in one direction of rotation thereof, causes successive engagement of contacts |69, which, in turn, causes a reduction in the resistance in series with the motor 80 to increase the speed oi' the motor in proportion to the existing off-.speed condition.

The first pair of contact arms |69 carries an additional set of contacts |10-|1|, which, when closed, connects the other side o! the eld of follow-up motor 50 through conductor |64 to ground. 'Ihe contacts |10|1| are closed substantially simultaneously with the closure oil the first pair of contacts |69.

The positive terminal of battery 18 is connected by means of conductor 10 directly to the armature lead of servomotor 60 and a branch thereof is connected to the outer end of the serially connected resistance units |13 of speed-control unit |15. 'I'he speed-control unit |15 has a contact unit |16 consisting of the'ilexible contact arms |18, having contacts |19 adapted to be successively closed by depression of the plunger |11 by cam I5 The mst pair of contacts |16 serves as a switch to connectthe armature lead 16 of follow-up motor 50 to the battery lead 10 through the entire resistance unit |13, and as the plunger |11 is depressed, the resistance in series with the follow-up motor 50 is progressively decreased, allowing the motor to increase its speed.

Operation 0f the device of Fig. 8

The operation of the device of Fig. 8, vtaken in conjunction with the circuit diagram Fig. 9, is similar in most respects to the operation of .the embodiment of Fig. 1 in that, when shaft 26, for example, increases its speed from the predetermined value, the increase will be reflected through differential I5 to shaft |0, which will cause differential side gear |42 to rotate at-a greater rate than side gear |4| so that the carrier |44 rotates counterclockwiselooking to the left in Fig. 8, which will cause helical gear. |45 to drive mating helical gear|46 in a counterclockwise direction as seen in Fig.' 8, causing cams |50 and |5| to rotate4 or contacts les cf the speed-contra una lss wm close, causing servomotor 60 to operate ina direction to cause the speed-control means of the prime mover or other controlled device (not therewith, the contacts |60-|6| are closed to energize the follow-up motor 50, which feeds its revolutions through differential |5 to restore the differential carrier |44 to its neutral position. Upon the first closure of the contacts controlling the servo and follow-up motors, cam-operated plunger |11 closes the rst pair of contacts |19, to insert a maximum of resistance in the followup motor circuit, so that, both the servo and follow-up motors operate at a minimum rate. Upon return of the differential carrier |44 to the neutral position, if there is still an uncorrected speed difference, the cycle will be repeated, but if the speed change or off-speed is suiflciently high in value, the follow-up will not be able to return the differential carrier to the neutral position, and a further set of contacts |59 and |19 will be engaged,-

cutting out resistance in the servomotor and follow-up motor circuits,'allowing their respective speeds to increase, and if this speed is insufhcient, resistance will be progressively removed until the maximum speeds of these motors are reached, and if the magnitude of the speed change is not then reduced to the point where follow-up motor 50 can restore the differential carrier |44 to the neutral position, stop |52 will engage the contact plunger |51 to stop further rotation of the cams, and the friction drive thereof from shaft |41 will permit the shaft to slip. By proper design of the resistance units of the motor speed-controls, the servomotor and follow-up motor speeds can be so controlled, through the speed-control means therefor, that the approach of the controlled device to the predetermined speed will be through a series of control cycles during each of which the rate of correction will be nearly proportional to the existing off-speed, and the rate of correction will decrease as equilibrium is approached, definitely eliminating hunting. By varying the amount of resistance shorted out at each successive step by contacts |19, the follow-up characteristics may be varied to conform to any particular governing requirement.

If the speed of shaft 26 decreases from the predetermined constant speed as determined by the speed setting'of motor 2, the differential carrier |44 will rotate in a reverse sense from that as above described, causing gear |48 and cams |50 and |5| to rotate in a clockwise sense as seen in Fig. 8, causing plunger |61 to be depressed to start servomotor 80 and follow-up motor 50 in the reverse direction through the medium of the speed-control unit |65, in the same manner as above described with reference to the action of control unit |55. `As the plunger |61 is depressed, the speed of servomotor 80 is increased, due to the cutting out of resistance in the circuit thereof,

4and simultaneously, cam |5| will depress the plunger |11, which will cut out resistance in series with follow-up motor 50. The servomotor 80 will operate in a reverse sense to increase the speed of the controlled device till the equilibrium speed is reached in exactly the same manner as above described with reference to the increased speed condition.

It is obvious that the speed-control units |55 and |65 may be replaced by switches operative to start the servo and follow-up motors in the forward and reverse sense of rotation respectively, the servomotor operating at its maximum rate at all times to effect, for example, propeller pitch change, and speed-control unit may be em.. ployed to vary the follow-up motor speed in the same manner as above described.

A further embodiment of the invention in which the speeds of the servomotor and follow-up motor are automatically varied is illustrated in Fig. 10, and this embodiment is similar to the device of Fig. 8, except that hydraulic servo and follow-up motors are employed in place of electric motors.

Referring now to Fig. l0, it is seen that the governor therein disclosed has the parts including constant-speed motor 2, input shaft 26, fol* low-up differential I5, speed-diiference-detecting differential |40, helical gear |45 driven by the differential carrier |44 and control-actuating gear |46 meshing therewith, identical with the construction illustrated in Fig. 8. The shaft |41 driven by gear |46, drives the fibre sleeve |48y which, in turn, frictionally drives the hub |49 similar to the device of Fig. 8. The remaining structure related to hydraulic control which differs from the embodiment of Fig. 8, will now be described.

The hub |49 has mounted thereon a cam |88, having at the left portion thereof a neutral point a, a zone of increasing radial dimensions from point a to a stop portion IBI, and a zone of decreasing radial dimensions from point a to a second stop portion |82. The cam portions above noted cooperate witha cam follower roller |85 engaging the periphery thereof, the roller being adapted to reciprocate a valve stem |86, the roller being urged into contact with the cam by means of a loading spring |81 Aacting on the valve stem. The valve stem |86 is connected to a conventional spool-type, balanced pressure, piston valve |88, having a central drain passage |89 therethrough,v the valve being reciprocable in a cylindrical bore in a valve body |90. The piston valve |88'is adapted, upon being shifted in either direction from the neutral position, to admit fluid under pressure from a conduit 9|, which receives said fluid from a pump |92 provided with a pressure relief valve |93, to either one of a. pair of conduits |94 and |95, the other conduit of the pair being connected through the valve to a conduit |96 which returns discharged fluid to a reservoir (not shown) from which pump |92 derives its fluid supply.

The conduits |94 and |95 are connected to a reversible hydraulic servomotor |91 which may be of the simplevgear type and adapted to run in one direction upon admission of motive fluid from conduit |94 and to run in the reverse direction upon admission of motive fluid from conduit |95. The servomotor |91 has an output shaft |98 which drives a Worm 82 which in turn through a gear sector 83 actuates the control lever 85 as in the device of Fig l to thereby control a prime mover or other device to be governed.

The cam |86 has a second neutral point b at the right hand portion thereof and increases in radius from point b to stop |8| and decreases in radius from point b to stop |82. The right hand portion of the cam is generally similar to the right hand portion but the cam contour may be varied to suit the particular relation of the follow-up rate to the existing value of the off-speed condition. A roller type cam follower 200 cooperates with the right hand portion of the cam and is adapted to actuate a valve spindle 20| against the resistance of a return spring 202. The spindle 20| forms a part of a control valve assembly gener-ally indicated at 205 identical in construction with the left hand control valve. The control valve 205 contains a valve (not shown) shiftable by spindle 20| andadapted when shifted in either direction from the neutral position to admit fluid under pressure from a a,seo,oes 1 1 conduit 200 to either one of a pair f conduits 201 and 200 which are connected to a reversible hydraulic follow-up motor 209 and connecting the other oneof the pair of 'conduits to drain via the control valve 205 and a drain conduit k2|0 connected thereto from whence the fluid returns to the supply reservoir (not shown). The conduit 206 is connected to the conduit 9| to receive fluid under pressure therefrom delivered by pump The follow-up motor 209 is adaptedto impart a follow-up drive through ldifferential Il by means of a shaft 20 and gear 21 similar to the device of Fig. 8 the direction of rotation of the Uperation The operation of the device of 10 is generally similar to that of the embodiment of Fig.

8 in that the differential Vcarrier |40 will rotate,

for example, in a direction to rotate gear |40 in a counterclockwise direction upon an overspeed- `ing of shaft 26 from the desired constant speed,

as determined by the speed of motor 2. The displacement of gear 4|46 as described, will cause cam |00 to rotate in the same sense and cause valve |09 to be moved to the left from the neutral position as seen in Fig. 10, connecting conduit |95 to receive fluid under pressurefrom conduit |9| in a volumetric quantity dependent upon the amount of valve movement. The conduit |93 is connected to drain through the passage |89 in the valve body. The fluid under pressure delivered through conduit |95 will cause motor |91 to rotate in a direction to cause the device being governed to reduce its speed. The speed of motor |91 for a given capacity is dependent upon the displacement of valve |88 from its neutral position and the rate of operation of the servomotor will be dependent on the angular displacement of the cam |00 which in turn is a function of the existing off-speed condition.

Simultaneous with the movement of valve |00 the cam follower 200 will move to the left from the position shown in Fig. 10 causing valve 209 to admit fluid under pressure into conduit 201 energizing follow-up motor-209 which will cause the carrier of differential H0 to be returned to the neutral position and thus initiating a cyclical control in the same manner as in the previously described embodiments. The displacement of the valve spindle and of the control valve element of the valve assembly 205 is also dependent on the angular rotation of the cam |80 and hence the quantity of fluid admitted to follow-up motor 209 and the follow-up rate will be a function of the olf-speed though not necessarily varying in the same relation as the servomotor speed, The time duration of the control cycles will vary as function of the oil-speed dependent on the particular contour chosen for the right hand portion of cam |90 which may be made to conform with the governing characteristics desired.

When the character of the on-speed is an un-v derspeed condition the cam |00 will rotate in the opposite sense causing the control valve elements to be displaced in the opposite directions from that as above described reversing the operation of the servo and follow-up motors.

the carrier of differential to the neutral position, the stops |0| and, |02 will be engaged by the respective cam followers and the friction coupling I will permit slipping, the servo and follow-up motors then continuing to operate at their maximum rates until the servomotor has enected a suilicient speed 'correction to enable the follow-up motor to restore the differential carrier to the neutral position and initiating the cyclical control until the equilibrium speed is reached. e

While the present invention is concerned with the construction of a novel differential speed responsive device it is to be understood that conventional limit switches may be employed where the application of the device as a governor rey qulres such elements.

. to phase angle with a reference speed shaft with- While the present invention is primarily concerned withspeed control and synchronizing as to speed, experiments with a governor in accorciance with the invention have shown that the control is suillciently sensitive to maintain the driven shaft of a controlled device constant as in a range of ten degrees, and which figure could be reduced by employing a finer pitch screw for the .pinion nut and increasing the sensitivity of the control switches, the only limiting factor being the ability of the device being controlled to lrespond to vary small' control impulses. These tests have demonstrated that speed responsive `mechanism constructed in accordance with the invention is applicable to control of the roll drives of rolling mills, paper mills. winding and reeling devices, conveyors and the likeand such use is contemplated in the broad aspects of the inven- 1. A speed `responsive device comprising: a`

three-element differential having driving means In the event that the off-speed condition is ,f arate power means being selectively energized in response to the departure of said differential third element from the neutral position and causing a restoring effect through said differential to' return said differential third element to the neutral position.

2. A differential speed'responsive device comprising: a first differential having a first element, a rotary input shaft for driving said first eiement, a second element, arotary shaft for drlving said second element, and a third element movable from a predetermined neutral position in response to the difference in speeds of said first land second differential elements, servo mechanism controlled by said third element in response to departure thereof from the neutral position, a second diiferential having two input drives and an output drive, the speed of rotation of the output drive being in accordance with the algebraic sum of the respective input drives of said second differential, a driving connection between the output drive of said second dinerential and the rotary input shaft for driving the second element of said nrst differential, means for driving one of the input drives of said second differential in accordance with the rotational speed of a device to be controlled, reversible motor means for driving the other of the input drives of said second differential, and means for energizing said reversible motor means in response to departure of the third element of said first differential from the neutral position.

3. The structure as claimed in claim 2, including means for controlling the rate of operation of said reversible motor means in accordance with the magnitude of the departure of the third element of said ilrst differential from the neutral position.

4. The structure, as claimed in claim 2, including means for controlling the rate of operation of said servo mechanism in response to the magnitude of the departure of the third element of the rst differential from the neutral position, and means for controlling the rate of operation of said reversible motor means in accordance with the departure of the said third element of the iirst dinerential from the neutral position.

5. A differential governor for the control of a prime mover or the like, comprising: a threeelement differential having one element thereof driven at a constant speed, a second element 'having a two-way driving means therefor, a third tion, said two-way driving means for said differential second element including one drive adaptedto-be rotated at a velocity proportional to the speed of the device being controlled, and a second drive adapted to algebraically impose its speed upon the output drive of said two-way drive, to thereby tend to restore the third element of said diiferential to the said neutral position, and means for energizing said second drive upon displacement of said third element from the said neutral position.

6. In a differential speed responsive device, a three-element speed-comparing means, having a first speed input drive, a, second speed input drive and an element movable from a predetermined neutral position in accordance with the dinerence in speeds between said first and second input drives, speed control mechanism controlled by departure of said element from the neutral position, a follow-up drive associated with one of said differential input drives operative to restore the said element to the neutral position after a displacement thereof from the neutral position, said follow-up drive being controlled in response to the departure of said element from the neutral position and operable at a rate independent of the rate of operation of said speed control mechanism, and rate of change of speed responsive means associated with one of said diierential input drives and operative in response to a rate of change of speed thereof in aandoet excess of a predetermined vaine to cause operation of said speed control mechanism irrespective of any control exerted thereon by said dinerential element.

7. A governor of the class described, comprising: a differential having a first element, a constant speed motor for driving said first element, a second element, an input driving shaft for said second element, a third element,' movable in either of two directions from a predetermined neutral position in accordance with the difierence in speeds of said rst and second elements, a second diierential having a separate pair of input drives and an output drive rotatable in accordance with the algebraic sum of the speeds of said input drives, a connection between the output drive of said second differential and the input driving shaft of said second element of said iirst-named differential, means for driving one of the input drives of said second differential at a speed dependent on the speed of rotation of a device to be governed, a reversible follow-up motor for driving the other of the in` put drives for saidsecond differential to vary the speed of the output drive of said second differential to cause a restoring effect on the third y, element of said first-named differential tending to departure thereof from the said neutral posii to restore the same to the neutral position upon a. displacement therefrom, a reversible servomotor adapted to actuate the speed-controlling means of a device to be governed, and control means actuated by the said third element of said first-named differential upon displacement of said third element from the neutral position, said control means being operative to selectively and simultaneously control the energizing said servoinotor and said follow-up motor.

8. In a differential ,governor of the character in which the differential compares aninput rotational speed of the device to be governed with an input reference speed and having a movable element operative upon displacement from a predetermined neutral position to control the positioning of a speed control element in accordance with the measured speed difference; the improvement, which comprises: a reversible iollow-up power drive, operatively associated with one of the inputs of said differential for algebraically superimposing its speed on said input to produce an eiect restoring the differential control element to the predetermined neutral position, said follow-up drive being independent of the rate of operation of the speed control element, and means for energizing said follow-up drive in response to the departure of the movable element from a predetermined neutral position.

9. 'I'he structure as claimed in claim 8, in which the means for actuating the speed control element includes a reversible electric servomotor switch-control means for selectively energizing said servomotor, said switch means being selectively actuated by said differential movable element and said reversible follow-up drive including a reversible electric motor selectively controlled as to the energization thereof by said switch-control means, the rate of operation of said follow-up motor being independent of the rate of operation of said servomotor.

10. The structure, as claimed in claim 8,- in which the means movable in accordance with the measured speed difference includes a hy- 'draulic control valve means, operative to control the neutral position in response to movement of the said differential movable element in accordance with the said measured speed dii'ference.

l1. A proportionalizing diilerential speed responsive device comprising: a three-element differential having a first element adapted to driven at a constant speed, a second element adapted to be normally driven at a speed proportional to the instant speed of a device to be controlled, and a third element movable from a predetermined neutral position in accordance with the difference in speeds of said iirst and second elements, reversible servo mechanism selectively energized by departure of said third element from the neutral position, a two-way drive including a pair of input drives and an'output drive, a connection between said output drive and the second element of said differential said input and output drives being constructed I and arranged lsuch that said output drive is in accordance with the algebraic sum of the input drives, one of said input drives being adapted to be driven at a'speed proportional to the speed of the device to be controlled, reversible power means for driving the other of said input drives at a rate independent of the operation of said servo mechanism, means for selectively energizing said power means responsive to departure of said differential third element from the neutral position to thereby cause a follow-up effect through said diiferential restoring said differential third' element to the neutral position and deenergizing said servo mechanism and said reversible power means, a further existing speed difference causing a cyclical repetition of the operation of said servo mechanism and reversible power means, the time duration of each cycle of operation being proportional to the existing dii'- ference in speed between said differential ilrst and second elements.

12. The structure as claimed in claim 11,*in which said one of the input drives of said ,twoway drive includes a slip drive having a torque transmitting capacity substantially greater than the torque required to overcome friction in said two-way drive and the differential elements connected thereto and driven thereby, but said slip drive being adapted to slip upon development of a resisting torque exceeding the capacity of said drive.

13. In a differential governor, a constant reference speed driving meanameans driven at a speed proportional to the speed of a device to be controlled, speed difference comparing means operatively connecting said reference speed driving I means and said means driven in accordance with the speed of the device to be controlled, said speed comparing meansincluding an element movable in either of two directions from a predetermined neutral position respectively upon an increase or decrease in the speed of the device being controlled from the desired constant speed, speed control servo mechanism selectively energized under the control of said element upon departure thereof from the neutral position and means selectively controlled by said element upon departure ment of said speed dinerence comparing means to the neutral position includes motor means operable at a substantially constant rate and selectively energized upon departure of said element from the neutral position under control thereof, and deenergized upon restoration of said element to the neutral position.

15. The structure as claimed in claim 13 in which the means for restoring the movable element of said speed difference comparing means to the neutral position includes motor means operable at a rate substantially proportional to the value oi' the speed difference and selectively enerv gized upon departure of said element from the neutral position under the control thereof, and deenergized upon restoration of said element to the neutral position.

16. A differential speed responsive control system comprising a three element differential having a first rotatable element, a. constant speed drive for said first element, a second rotatable element, a means for driving said second element in accordance with the speed of the device to be controlled, a third element selectively displaceable from a predetermined neutral position upon the occurrence of a difference in speed between the constant speed drive and the means for driving said second element. servomotor control means adapted to be actuated by said third differential element upon displacement thereof from the neutrai position, follow-up means adapted to physically restore the differential third element to the neutral position independent of the equalization of speeds between the respective driving means for said differential first and second elements, and means actuated by displacement of said differential third element from the neutral position for selectively controlling the follow-up means.

'HOWARD M. McCCY. 

